U.S. patent number 4,455,479 [Application Number 06/366,669] was granted by the patent office on 1984-06-19 for electric oven toaster.
This patent grant is currently assigned to Tokyo Shibaura Denki Kabushiki Kaisha. Invention is credited to Takehiko Itoh, Moriyoshi Sakamoto.
United States Patent |
4,455,479 |
Itoh , et al. |
June 19, 1984 |
Electric oven toaster
Abstract
A cooking appliance comprising a heating chamber with a window
provided on one side. At least one surface of the window is coated
with a film of a reflecting metal oxide, such as indium oxide, to
such a thickness that food in the heating chamber can be seen
through the window.
Inventors: |
Itoh; Takehiko (Yokohama,
JP), Sakamoto; Moriyoshi (Yokohama, JP) |
Assignee: |
Tokyo Shibaura Denki Kabushiki
Kaisha (Kawasaki, JP)
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Family
ID: |
11706630 |
Appl.
No.: |
06/366,669 |
Filed: |
April 8, 1982 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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169171 |
Jul 15, 1980 |
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5679 |
Jan 23, 1979 |
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Foreign Application Priority Data
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Jan 31, 1978 [JP] |
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53-8939 |
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Current U.S.
Class: |
219/405; 99/447;
126/200; 219/408; 219/411; 219/521; 359/359; 392/422 |
Current CPC
Class: |
A47J
37/0635 (20130101); F24C 15/04 (20130101); C03C
17/245 (20130101); C03C 17/3417 (20130101); C03C
2218/151 (20130101); C03C 2217/215 (20130101); C03C
2217/94 (20130101) |
Current International
Class: |
A47J
37/06 (20060101); F24C 15/04 (20060101); F24C
15/02 (20060101); F27D 011/00 () |
Field of
Search: |
;219/219,1.55D,405,411,408,521,214,347,543,392,395 ;126/200 ;65/6D
;99/447 ;350/1.60 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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2417927 |
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Oct 1974 |
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DE |
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795912 |
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Jun 1958 |
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GB |
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1339469 |
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Dec 1973 |
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GB |
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1341616 |
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Dec 1973 |
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GB |
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1392458 |
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Apr 1975 |
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GB |
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1417333 |
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Dec 1975 |
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GB |
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2013874 |
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Aug 1979 |
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GB |
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Other References
Toshiba Brochure, #55K160 and 54K518..
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Primary Examiner: Mayewsky; Volodymyr Y.
Attorney, Agent or Firm: Oblon, Fisher, Spivak, McClelland
& Maier
Parent Case Text
CROSS REFERENCE TO RELATED APPLICATIONS
This application is a continuation of U.S. Ser. No. 169,171 filed
July 15, 1980, now abandoned, which was a continuation-in-part of
U.S. Ser. No. 5,679 filed Jan. 23, 1979, now abandoned.
Claims
What is claimed as new and desired to be secured by letters patent
of the united states is:
1. An electric oven-toaster adapted for toasting a slice of bread,
comprising:
a housing enclosing a heating chamber, said housing having a front
wall;
a glass window, which can be freely opened and closed, forming part
of said front wall of said housing;
food holding means disposed horizontally within said heating
chamber;
heating means disposed within said heating chamber for generating
infrared rays, said heating means being parallel with both the
inner surface of said glass window and said food holding means;
a metal holding reflecting plate disposed within said heating
chamber and bent in a manner to surround said heating means and
said food holding means to reflect said infrared rays generated by
said heating means such that said reflected infrared rays are
substantially uniformly distributed on said food holding means;
and
an infrared reflective film of metal oxide formed on the entire
inner surface of said glass window; said glass window being
positioned in a manner to provide a predetermined free space
between the side edge of said food holding means on the side of
said glass window and the lower edge of said glass window and being
inclined in a manner to reflect said infrared rays toward said free
space and said food holding means.
2. An electric oven-toaster according to claim 1, wherein said
means for supporting food has a plane surface on which said food is
placed.
3. An electric oven-toaster according to claim 2, wherein said
heating means is comprised of two electric heaters disposed above
and below said supporting means respectively.
4. An electric oven-toaster according to claim 3, wherein said
metal oxide film is an indium oxide film of 1500 to 3000.ANG.
thick.
5. An electric oven-toaster according to claim 4, wherein a silica
film is formed on the surface of said indium oxide film.
Description
This invention relates to a cooking appliance and more particularly
an electric oven toaster having a window through which it is
observed how food in the appliance is cooked.
Known cooking appliances such as oven-toasters have a window with a
transparent glass pane so that it can be seen how bread, for
example, is toasted in the appliance. The glass pane prevents heat
from escaping from the appliance. The glass pane occupies a greater
part of the front of the cooking appliance. Some of the radiation
energy generated inside the appliance dissipates inevitably through
the window. This means a loss of heat. Due to the dissipation of
heat a temperature gradient takes place inside the appliance. That
is, the temperature is low near the window and high near the rear
of the appliance. Consequently the food cannot be heated uniformly,
some portion overcooked and other portion undercooked.
An object of this invention is to provide an electric oven toaster
which reduces loss of radiation energy through a window thereby to
use heat effectively and which can cook food as uniformly as
possible.
An electric oven toaster according to this invention has a window
with a transparent pane which is coated at least on one surface
with a metal oxide material to such a thickness that food in the
appliance can be seen, said metal oxide material reflecting thermal
radiation generated in the appliance.
Indium oxide or the like is used as the metal oxide material. If
the indium oxide is used, it is preferred that indium oxide be
coated 200.ANG. or more thick on the transparent pane. If the metal
oxide material is coated too thick, it would make it impossible to
clearly observe food in the appliance. Thus, indium oxide is coated
5000.ANG. thick at most, preferably 1500 to 3000.ANG. thick. On the
film of the metal oxide material thereby may be coated a
light-permeating protective film of, for example, silica
(SiO.sub.2).
This invention can be more fully understood from the following
detailed description when taken in conjunction with the
accompanying drawings, in which:
FIG. 1 is a cross sectional view of an electric oven toaster
according to this invention;
FIG. 2 is a cross sectional view of the transparent window pane of
the appliance shown in FIG. 1;
FIG. 3 is a cross sectional view of a modification of the
transparent window pane shown in FIG. 2;
FIG. 4 is a graph showing the heat-preserving characteristic of an
electric oven toaster according to this invention and that of a
conventional cooking appliance;
FIG. 5 is a photograph of slices of bread toasted by a conventional
oven-toaster;
FIG. 6 is a photograph of slices of bread toasted by an
oven-toaster according to this invention; and
FIG. 7(I) is a photograph of a slice of bread toasted by a
conventional oven-toaster; and
FIG. 7(II) is a photograph of a slice of bread toasted by an
oven-toaster according to this invention.
Now referring to FIGS. 1 and 2, an oven-toaster, an embodiment of
this invention will be described. The oven-toaster comprises a
housing 1 having a window 14 on one side. All the inner surface of
the housing 1 is covered with a reflecting plate 2 which is plated
with nickel, chromium or the like. The plate 2 is so bent and
curved that infrared rays are reflected and distributed uniformly
to a food table 3 which is housed in the housing 1. An elongated
electric heater 4 is provided above the food table 3, and another
elongated electric heater 5 below the food table 3. The heaters 4
and 5 extend generally across the length of the oven-toaster. Each
heater has a longitudinal axis which is positioned in a parallel
relationship with respect to the window 14 and to the food table 3.
These heaters 4 and 5 are so positioned as to apply infrared rays
uniformly to the food table 3, directly or indirectly. The window
14 is constituted by a frame 6 and a transparent pane 7 made of,
for example, heat-resistant glass. The transparent pane 7 is hinged
to the frame 6 so that it can be opened and closed. Attached to the
pane 7 is a handle 9.
As illustrated in FIG. 2, the transparent pane 7 is constituted by
a semi-tempered glass plate 10 and a film 11 of a metal oxide
material such as indium oxide. The film 11 is laid on one surface
of the glass plate 10 and formed by vacuum vapor deposition to such
a thickness that food on the food table 3 can be seen through the
pane 7. Futher, as shown in FIG. 3, a transparent protective film
12 made of silica or the like may be laid on the film 11 thereby to
prevent a wear of the film 11 and thus prolong the life thereof.
The protective film 12 serves to increase the mechanical strength
of the transparent pane 7. The protective film 12 can be easily
formed by known methods such as sputtering, spraying and chemical
vapor deposition. By such method the film 12 can have a uniform
thickness, and any portion of it transmits the same amount of
light.
On the food table 3 of the oven-toaster of the above-mentioned
construction a slice of bread 13 is placed. Both electric heaters 4
and 5 are then turned on to emit infrared rays. Some infrared rays
from the upper heater 4 impinge directly on the bread 13 to heat
the upper surface portion of the bread 13, as arrow A in FIG. 1
indicates. The remaining infrared rays from the heater 4 are
reflected on the reflecting plate 2 as depicted by arrow B or on
the metal oxide film 11 as indicated by arrow C and then heat the
upper surface portion of the bread 13. Most infrared rays from the
lower heater 5 heat the lower surface portion of the bread 13,
either directly or after being reflected on the reflecting plate 2,
as illustrated by arrows D in FIG. 1. Thus, some of the infrared
rays emitted from the heaters 4 and 5 to the transparent pane 7 are
reflected on the metal oxide film 11 so as to heat the slice of
bread 13. As a result, the temperature rises quickly even near the
transparent pane 7, whereby the bread 13 can be uniformly
heated.
To demonstrate that the temperature inside the oven-toaster
according to this invention is elevated quickly and that the
reflected infrared rays effectively work to heat the food, the
following experiment was conducted. A slice of bread was toasted by
the oven-toaster of this invention. Then the transparent pane 7
became clouded up with moisture emitted from the bread about 15
seconds from the start of toasting. Next, a slice of bread was
toasted by a known oven-toaster the window glass plate of which is
not coated with a metal oxide film. It was found that it took about
45 seconds until the glass plate was clouded up with moisture from
the bread. Obviously in the oven-toaster according to this
invention the infrared rays were reflected upon the metal oxide
film 11 and quickly raised the temperature inside the
oven-toaster.
Now referring to FIG. 4, the heat-preserving characteristic of the
oven-toaster according to this invention will be explained. FIG. 4
is a graph wherein the abscissa shows the thickness of a metal
oxide film formed on the glass plate 10 and the ordinate shows the
equilibrium temperature inside the housing 1. Curves A, B, C and D
show the heat-preserving characteristics of oven-toasters according
to this invention, and a straight line E shows the equilibrium
temperature, about 260.degree. C., inside a conventional 800 W
oven-toaster manufactured by Tokyo Shibaura Denki Kabushiki
Kaisha.
Curve A shows how the equilibrium temperature inside an 800 W
oven-toaster of this invention changed when the thickness of an
indium oxide (In.sub.2 O.sub.3) film on the inner surface of a
window glass plate was formed 200.ANG., 500.ANG., 1000.ANG.,
1500.ANG., 2000.ANG., 2700.ANG., 3200.ANG. and 5000.ANG.. As curve
A teaches, the equilibrium temperature reached a peak of
315.degree. C. when the indium oxide film was 2700.ANG. thick. This
peak temperature is 55.degree. C. higher than the equilibrium
temperature inside the conventional 800 W oven-toaster.
Curve B illustrates how the equilibrium temperature inside a 620 W
oven-toaster of this invention changed when the thickness of an
indium oxide (In.sub.2 O.sub.3) film on the inner surface of a
window glass plate was changed as mentioned above. The maximum
equilibrium temperature was recorded as high as 274.degree. C.
Apparently, the 620 W oven-toaster can preserve heat more
effectively than the conventional 800 W oven-toaster with a
transparent windowpane which is not coated with a metal oxide film.
It is also clear that the 620 W oven-toaster can save much power,
200 W or more, in comparison with the conventional 800 W
oven-toaster.
Curve C shows the equilibrium temperature inside an 800 W
oven-toaster of this invention changed when the thickness of an
indium oxide (In.sub.2 O.sub.3) film on the inner surface of a
window glass plate was changed as mentioned above and a transparent
protective film of silica (SiO.sub.2) was formed 1500.ANG. thick on
the indium oxide film. In this case, as curve C shows, the
equilibrium temperature was 40.degree. C. or more higher than that
inside the conventional 800W oven-toaster when the indium oxide
film was 1000.ANG. or more thick.
Curve D shows how the equilibrium temperature inside an 800 W
oven-toaster of this invention changed when a film of indium oxide
(In.sub.2 O.sub.3) was formed on the outer surface of a window
glass plate to the above-mentioned various thicknesses. In this
case the equilibrium temperature was found to be a little lower
than as illustrated by curve C. However, it is 25.degree. C. or
more higher than the equilibrium temperature inside the
conventional 800 W oven-toaster.
With reference to FIGS. 5 to 7 it will now be explained how many
slices of bread were toasted by the above-described 620 W
oven-toaster according to this invention and by a conventional 620
W oven-toaster manufactured by Tokyo Shibaura Denki Kabushiki
Kaisha, whose transparent windowpane is not coated with a metal
oxide film FIG. 5 is a photograph of two slices of bread toasted by
the conventional 620 W oven-toaster, and FIG. 6 a photograph of two
slices of bread toasted by the 620 W oven-toaster according to this
invention. Both oven-toasters were turned on with no bread inside
them, and the temperature inside them was raised until it reached a
temperature high enough to toast slices of bread. This sufficiently
high temperature was maintained in both oven-toasters. Then, slices
of bread were put into both oven-toasters at the same time, two
slices in each oven-toaster. As FIG. 5 illustrates, the slices of
bread taken from the conventional 620 W oven-toaster were toasted
substantially not at all at the portion K (lower end portion in
FIG. 5) which had been placed near the transparent window-pane. In
contrast, as shown in FIG. 6, the slices taken from the 620 W
oven-toaster of this invention were toasted brown and uniformly all
over its surface. The slices taken out of the conventional
oven-toaster were then further toasted by the oven-toaster. It took
the conventional oven-toaster more than 75 seconds to toast the
slices to the same brownness as the slices toasted by the
oven-toaster according to this invention.
FIG. 7(II) is a photograph of a slice of bread toasted by the 620 W
oven-toaster of this invention, spending time 75 seconds less than
the time which the conventional oven-toaster had spent to toast the
slice to such brownness as shown in FIG. 7(I). As FIGS. 7(I) and
7(II) clearly show, corner portions L and M of the slice taken out
of the conventional oven-toaster were toasted but insufficiently,
while all the corner portions N, O, P and Q of the slice taken from
the oven-toaster of this invention, as well as the central portion,
were toasted sufficiently to substantially the same extent.
Apparently the oven-toaster according to this invention is
advantageous over the conventional one in that it can toast bread
quickly and uniformly. That is, the oven-toaster can save much
power and can toast much bread in a given time.
As clearly understood from the above described embodiments,
according to this invention a metal oxide film may be formed on the
inner or outer surface of the transparent glass plate.
In the embodiment shown in FIG. 1 the transparent pane 7 is hinged
to the frame 6 and opened and closed so that food can be placed
within the oven-toaster. In other words, the pane 7 works not only
as a window through which food inside the oven-toaster is observed
but also as a door through which food is inserted into the
oven-toaster and taken out therefrom. Instead, a door may be
provided independently of the transparent pane 7. If this is the
case, the door need not, of course, be made of a transparent
material.
As mentioned above, the electric oven-toaster according to this
invention reduces heat loss and cooks food uniformly, and thus
effectively saves power. From an industrial point of view it is
therefore highly advantageous. Further, since the temperature
inside the electric oven-toaster rises fast thereby to cook food
quickly, little moisture escapes from the food so that the food is
cooked soft and full. In addition, the electric oven-toaster is
advantageous in that its transparent pane is not heated so hot as
those of conventional toasters. Still further, since these
advantages can be accomplished merely by substituting a glass plate
coated with a metal oxide film for a plain glass plate, without
re-designing the other parts of the toaster the assembly line for
the conventional electric oven-toaster of this type can be utilized
to manufacture the electric oven-toaster according to this
invention. This is another advantageous feature of the present
invention.
The glass plate coated with indium oxide, a constituent member of
the cooking appliance according to this invention, was tested in
accordance with Notice No. 370 of Ministry of Health and Welfare,
"Standards of Food and Additives--Utensils and Container Packing".
The test showed that no poisonous substance such as lead and
arsenic was detected from the glass plate.
* * * * *